An electrical supply typically serves loads which have a varying demand. As the demand changes, the current, which represents kinetic energy, must change. This presents a serious problem when a supply is operating at maximum current and the load is suddenly removed. A voltage transient occurs which may damage system components. Even when the source voltage of the supply is actively regulated, the regulator response time is finite and the voltage transient may not be completely controlled.
Transient suppression circuits have used a Zener diode clamp which conducts upon occurrence of an overvoltage condition. However, the typical Zener breakdown voltage varies with temperature. Where tight control of voltage transients is required, a Zener suppressor circuit is not satisfactory.
Nercessian U.S. Pat. No. 3,949,271 shows a transient suppressor circuit in which a differential amplifier is responsive to system voltage and with the occurrence of an overvoltage condition turns on a switch which conducts current through a shunt resistor circuit. The differential amplifier turns off, opening the switch, when the voltage returns to normal. The Nercessian circuit will stay on continuously as long as the voltage remains greater than normal. This operation may result in damage to the shunt resistor or the transistor with higher energy transients.